Control systems, for example those utilizing computers such as programmable logic controllers (PLCs), can control a broad number and type of devices, including alarms, indicators, actuators, motors, relays, and even input devices, such as sensors. Sometimes, such PLC's are located in remote locations, some of which are accessible via a cellular communications network.
To program, communicate with, and/or receive data from such a remote PLC, a user can access a local user interface device, such as a personal computer, which can be coupled via the cellular telephone network to a cellular modem coupled to the remote PLC. A power failure can cause the remote cellular modem to re-start. If the remote cellular modem requires that a password or other security code be entered at start-up in order to operate, a human local to the cellular modem typically must provide that security code to the modem. Only then can the modem be operable, and the connection established between the user's computer and the remote PLC.